1. Field of the Invention
The present invention relates to the preparation of high molecular weight organopolysiloxanes, and, more especially, to the preparation of such high molecular weight organopolysiloxanes by polymerization and rearrangement of low molecular weight organopolysiloxanes in the presence of an alkaline catalyst and an accelerator.
2. Description of the Prior Art
In published French Patent Application No. 2,353,589 (Application No. 76/17,170) there is disclosed a process for the preparation of high molecular weight organopolysiloxanes by the polymerization and rearrangement of cyclosiloxanes, optionally in the presence of low molecular weight, linear polysiloxanes. This process is characterized in that the polymerization reaction is carried out in the absence of solvent and in the presence of a catalyst system consisting of an alkali metal (or derivative thereof) and an oxygen-containing and/or nitrogen-containing mono- or polymacroheterocyclic compound (cryptand or crown ether), which acts as an accelerator. This process makes it possible to obtain a very high molecular weight polysiloxane using very small amounts of the catalyst system and with rapid kinetics. In a process of this type, however, it is necessary to employ macroheterocyclic compounds which have an extremely sophisticated and complex structure and, thus, which exhibit the disadvantages of requiring complex and intricate processes of synthesis and consequently are extremely expensive.
Serious need therefore exists in this art for an industrial process for the preparation of high molecular weight polysiloxanes by the polymerization of low molecular weight organopolysiloxanes, but utilizing an effective catalyst system which is much more readily available industrially.